The rapid development of multi-band composite detection technology has significantly enhanced the target detection capabilities of detectors, making traditional single-band stealth techniques inadequate in evading detection. Moreover, the increasing demand for multi-band integrated stealth technology in optically transparent scenarios, such as airplane portholes and automobile observation windows, has raised the need for higher transparency in stealth materials. Therefore, the design of multifunctional, ultrathin, and multi-band compatible wave-absorbing structures has become crucial. In this paper, we propose and successfully fabricate an ultrathin transparent absorber, with both infrared low emissivity and radar broadband absorbing performance. The structure consists of a multifunctional integrated metasurface layer, a high optical transparency dielectric substrate, and an all-reflective backplane. To verify the effectiveness of the absorber, a sample is prepared and systematically tested across visible, radar, and infrared wavelength bands. The results show that the metamaterial absorber designed in this paper exhibits excellent performance and demonstrates great potential for applications in daily life, medical diagnosis, aerospace, and military multi-band stealth applications.

In the design aspect, we employ commercial electromagnetic simulation software CST Studio Suite and MATLAB for joint modeling and simulation. MATLAB is used to first calculate the range of each parameter required to satisfy the condition of infrared emissivity <0.3, and then with the help of the Optimizer tool in CST, the parameters (P, L₁, L₂, L₃, Q, R, d) of the absorber are optimized. For electromagnetic simulations, a full-wave numerical simulation of the designed absorber is carried out using the finite element frequency domain module of CST. Floquet ports of transverse electric (TE) and transverse magnetic (TM) modes with normal incidence are set as excitation sources in the z-direction, using open boundary conditions, and periodic boundary conditions (unit cell boundary) are applied in the x and y directions to simulate an infinite periodic structure. For sample surface topography tests, dimensional parameters are measured using an Olympus optical microscope at 5× magnification. For microwave performance tests, the absorbance of the prepared absorber in the 6?14 GHz band is tested in a microwave anechoic chamber using the arch method. A pair of broadband horn antennas are connected to an Aglient vector network analyzer as the transmitting and receiving ends of the electromagnetic waves. The incidence angle of the electromagnetic waves is adjustable in the range of 0°?50°. For infrared performance, a Bruker Fourier transform infrared (FTIR) spectrometer is used to measure the transmission and reflection spectra of the metasurface functional layer. A FLIR infrared camera is also used to collect infrared images in the 8?14 μm band. To ensure uniform heating, a 60 mm×60 mm copper plate is placed as the homogenizing plate on the heating stage, which is set to 70 ℃. The metasurface functional layer of the absorber and a PET sample of the same size (30 mm×60 mm) are placed on the heating stage and heated together for 15 min, after which infrared photographs are taken with the FLIR camera. For visible light transmittance tests, a UV-2200 UV?visible spectrophotometer is used to measure the transmittance of the absorber in the 400?800 nm band.

The designed absorber achieves an absorption rate of more than 90% in the frequency range of 8.0?12.1 GHz, with a return loss of less than -10 dB. It demonstrates excellent impedance matching with free space in the operating frequency band (Fig. 2). The absorber also exhibits good stability with respect to changes in the polarization angle and incidence angle of the electromagnetic waves. It maintains more than 70% absorption in most of the operating frequency bands when the incidence angle is less than 50° (Figs. 3 and 4). Analysis of the contributions of different structural layers to the wave absorption performance reveals that the radar stealth primarily originates from the electromagnetic interaction between the ITO metasurface layer and the electromagnetic wave (Fig. 6). The distributions of surface electric fields and currents at the resonance frequency indicate the resonance modes and loss mechanisms (Fig. 7). Stability during the actual processing is verified by robustness analysis of the metasurface structural parameters (Fig. 8). A sample consisting of 10×10 cells is fabricated, and the UV?visible spectrophotometer is used to test the transmittance in 400?800 nm waveband (Fig. 9). The machining accuracy is measured using an optical microscope (Fig. 10), and the sample is tested using the arch method, infrared spectrometer, and imager. The test results for radar and infrared stealth are in excellent agreement with simulation predictions (Figs. 11, 12, and 14).

In this paper, we propose a sandwich-structured metamaterial absorber consisting of a double-layer low-square-resistance (<10 Ω/sq) indium-tin-oxide (ITO) film and a high-optical transparency dielectric substrate. This absorber combines low infrared emissivity, broadband microwave absorption, and high visible transmittance, with a total thickness of only 1.8 mm. Simulation results show that the absorber can achieve more than 90% of broadband absorption in the frequency band of 8.0?12.1 GHz, which completely covers the microwave X-band. Based on the theoretical design, the absorber is fabricated and achieves more than 90% broadband absorption in the 8.1?12.6 GHz range, with infrared emissivity in the 8?14 μm band of 0.249 and optical transmittance reaching 68.1%. All performance parameters are in excellent agreement with the theoretical simulation results, making the absorber a promising solution for multi-band composite stealth technology.